FIELD OF THE INVENTION
The invention relates to a circuit configuration for adjusting the quadrature-axis current component of a push-pull output stage having two transistors of opposite conduction type.
Such a circuit configuration is known, for instance, from Data Sheet NE/SA 5230 published by the firm Valvo on Nov. 14, 1986. In that device, a voltage across two series-connected diodes through which a reference current flows is compared with a sum of base-to-emitter voltages of the push-pull output stage transistors, and the quadrature-axis current component of the push-pull output stage is adjusted as a function thereof. Since the base-to-emitter voltages of the output stage transistors are proportional to the logarithm of the current flowing through them, the product of the current flowing through each of the output stage transistors is accordingly kept constant with respect to the logarithm of the reference current. In order to partially compensate for the temperature dependency of the logical relationship between the base-to-emitter voltage and the collector current in a transistor, the diodes have a corresponding temperature dependency. However, in order to attain greater accuracy a considerable additional expenditure for circuitry would be needed. Furthermore, in the known circuit configuration the accuracy is reduced even further by the fact that load changes, which influence the current in only one of the two output stage transistors, have an overall effect on the adjustment of the quadrature-axis current component, because of the product formed by the logarithmizing and ensuing addition.